They are edible and used in many places especially Korea, Philippines, China and Japan . Their flavor is slightly bitter but no more that most greens. They do add a peppery heat but no where near as much as the fruits

The leaves of at least some plants in the Solanaceae, the family to which peppers belong, are toxic: eggplants, potatoes, and tomatoes. I would assume that the leaves of pepper plants are also, unless proven otherwise.

One hint that it's so is the lack of recipes involving the leaves from chile plants, despite the peppers themselves having been used for millennia. But I'm not an authority on Mexican or Latin American cooking, so would be interested if anyone knows of a dish that does use pepper leaves.

This is when botanical names come in handy. As paulj notes, chefj's iinfo applies to some plants in the true pepper familly, Piperaceae. Jalapenos are a variety of Capsicum annuum, in the often-posonous-leafed and sometimes-poisonous-fruited nightshade family, Solanaceae.

Anyone know of recipes using the leaves of Capsicum plants? I'm always ready to learn, and to be surprised...